You can win points by either forcing errors or hitting winners. To force errors, you have to trouble the opponent in some way. One way to do is is to hit with more pace than they are used to which also gives them less time to set up - hitting flatter can help with that. Another way is to give them balls that are out of their preferred hitting zone - higher height with topspin or lower with slice. You can also make them move up/down or left/right to hit shots on the run which forces errors - high balls with topspin are good when you move them laterally and low balls with slice are good when you move them up.
To hit winners, you have to open up space and then hit winners into that open space. Both topspin and slice can be used to generate angles which open up space on the other side of the court. When you go for the winner, higher spin can give you more margin for error, but flatter shots can take away time - so, you have to decide on the right balance of pace and spin.
The strategies you have to win points are: change pace/spin, change depth, change ball height at contact for opponent, hit closer to lines or to smaller targets, have more shot tolerance on neutral balls, take away time, open up space, make them move more than they want to including up/down, use your serve to set up point patterns you like, use your return to set up point patterns you like, bring them to net if they don’t like it, go to the net yourself etc. Know your strengths and play to them. Find out your opponent‘s weakness and see if you can exploit them.
Spin is a tool that give you higher margin for error so that you can hit harder without making errors, allows you to hit to bigger targets and still trouble opponents, allows you to hit better angles to expand the court, allows you to change depth/pace without giving easy balls etc. Generally the better players hit hard with a lot of spin for their level and utilize both topspin and slice depending on which troubles their opponent more.